This invention is related to an active hand control system of the type wherein manual control input devices such as control sticks employed in a servo-coupled system are provided with an electrically-simulated variable rate feel. In particular, the invention relates to a system having a control stick such as is employed in aircraft, which is servo-coupled to the control system of the aircraft through electronics and a motor mechanism. The electronics and motor mechanism provide a simulated feel to the control stick when in operation which is similar to that of a purely mechanical system.
Servo control technology is well developed as applied in use in the field of robotics. In particular, electrical motor and servo control systems have been developed and employed in the past in the design of robotic hand controllers which are capable of reflecting forces experienced at the robotic end, back to, for example, a human operator.
One example of the type of control system to which the present invention is directed is disclosed in U.S. Pat. No. 4,150,803, which teaches a control stick for an operator having an electro-simulated variable rate feel. The simulated feel of the device of U.S. Pat. No. 4,150,803 is provided by a system which generates for the operator at the control stick the proper force and feel characteristics when used to control a boom employed during refueling operations between aircraft in flight.
These types of controllers generally involve the use of a control stick which is actuatable in at least two mutually perpendicular planes to provide both vertical and lateral control of the device being controlled. This invention could be appplied to controllers moveable in three rotational or three transtational axes with up to six degrees of freedom. An example of a two degree of freedom control stick is shown in U.S. Pat. No. 3,270,260 in which the control stick of the device has electrical pickup means in plate form, for example, capacitance bridge circuits arranged in a symmetrical arrangement such that a force exerted on the stick having a symmetrical arrangement of circuits unbalances them and produces a signal which is proportional to the force on the stick. The signals generated by the electrical pickups are used to generate output signals through appropriate and conventional electronics, which command a control actuator to effect control of the device being controlled.
Typically, in these systems the control stick is mechanically coupled at its axis to at least one motor which applies either a resisting force on the control stick or, in response to a signal produced by sensors that detect forces applied to the device surfaces being controlled, drives the control stick and in turn, drives the device being controlled to alleviate forces generated by the device under control as felt by the operator.
These types of controllers are particularly desirable for use in the operation of modern day aircraft, in particular, in the form of control sticks or yokes. In operation, the devices as used in the cockpit of aircraft are typically designed to exhibit some desired force versus displacement characteristics to the user whereby the magnitude of the control stick displacement is proportional to the force applied. The pilot controller produces as its output an electrical signal corresponding to the control stick position, and the signal is used to control the aircraft through the action of various motors and mechanical means, in a manner which is well known to those of ordinary skill in the art and is conventional. Thus, in use such systems provide an electronically controlled manual input control stick having force feel characteristics like those of purely mechanically linked systems. These applications in aircraft are typically referred to as "fly by wire" applications. Examples of presently existing applications of this technology are the systems employed in the Airbus A320 Transport Aircraft, the General Dynamics F16 Fighter aircraft and the NASA Space Shuttle.
In the past, in order to enhance or improve the force feel characteristics of such simulated feel control sticks, controller electronics were employed in combination with sensors for detecting the position of the control stick. A signal was generated and processed by controller electronics to drive a motor which in turn drove the control stick to simulate the feel of a mechanical system. Such controller electronics also included input from the system being controlled such as, for example, an auto pilot system or any external forces acting on the flight control surfaces of the aircraft which would, as a result of feedback and input from the surfaces, be input into the controller electronics to be reflected through the motor connected to the control stick at the user location.
While the use of a feedback loop in which the position of the control stick is detected and a signal resulting therefrom is processed by controller electronics to result in a control of a motor to which the control stick is connected to achieve force and feel characteristics typical of a mechanical system has been known, the position detection alone still fails to fully achieve the desired force feel characteristics typical of mechanical systems.